Phase shifter

ABSTRACT

A phase shifter includes first and second mixers which mix a first signal with a second signal having a phase different from the first signal, respectively, third and fourth mixers which mix the second signal with the output signals of the first and second mixers and a combiner which combines the output signals of the third and fourth mixers to produce an output signal having a phase which is inverted with respect to the first signal.

BACKGROUND OF THE INVENTION

This invention relates to a phase shifter for generating a signal whichhas a phase opposite to that of another signal.

DESCRIPTION OF THE PRIOR ART

Conventional phase shifter circuits generally employ either a circuitusing delay lines or a circuit using variable capacity diodes. However,the phase shift is stepwise in the former phase shifter, and the phaseshift can be continuous but has a narrow range in the latter phaseshifter.

As a result, in a case where a signal B is to have its phase invertedfrom that of another signal A, such a large phase shift is effected by acircuit employing a combination of delay lines and variable capacitydiodes. Smaller phase shifts can be produced by a circuit employingvariable capacity diodes alone. However, while phase shifters of thekind referred to above can be effective in producing variable phaseshifts within a limited range, it is difficult to effect phase shiftswhich vary over a wide range with such circuits.

SUMMARY OF THE INVENTION

An object of this invention, therefore, is to provide a phase shifterfor shifting one of two signals which have a phase difference from eachother to allow it to have a phase opposite to that of the other signal.

In order to achieve the above object of the present invention, a phaseshifter is provided comprising first and second terminals for receivingfirst and second signals having a phase difference from each other,first mixing means for mixing the first signal with the second signal,means for displacing the phase of the first signal by 90 degrees toproduce a first phase-displaced signal, second mixfng means for mixingthe first phase-displaced signal with the second signal, third mixingmeans for mixing the second signal with an output signal provided fromthe first mixing means, means for displacing the phase of the secondsignal by 90 degrees to produce a second phase-displaced signal, fourthmixing means for mixing the second phase-displaced signal with an outputsignal provided from the second mixing means and combining means forcombining an output signal of the third mixing means with an outputsignal provided from the fourth mixing means to generate a signal whichhas a phase opposite to that of the first signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing is a circuit diagram showing one embodiment ofthe phase shifter according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of a phase shifter according to the present invention willbe described in the following with reference to the circuit diagram ofthe drawing.

First and second signals e₁ and e₂, which have different phases withrespect to each other, are introduced from the terminals 2 and 4. Thefirst signal e₁ is supplied to a 90 degrees phase splitter 40A and isdivided thereby into two signals e₁₁ and e₁₂. Signal e₁₁ is in phasewith the first signal e₁, while the phase of signal e₁₂ is displaced 90degrees with respect to the first signal e₁. The signals e₁₁ and e₁₂provided from the splitter 40A are supplied to a pair of balanced mixers41 and 42, respectively. The signal e₂ which is split at a node N issupplied to an in-phase splitter 40 as a third signal e₃. This thirdsignal e₃ is divided into two in-phase signals e₃₁ and e₃₂. Thesesignals e₃₁ and e₃₂ are supplied to the mixers 41 and 42, respectively,and are mixed with the signals e₁₁ and e₁₂.

As a result, the mixed signals EI and EQ, which have frequencies of thesum or difference of two signals introduced in the mixers 41 and 42, areprovided from the mixers 41 and 42. The mixed signals EI and EQ and arefed through low-pass filters 51 and 52, respectively, to the amplifiers54 and 53. The gain of amplifiers 54 and 53 is set -A and A,respectively. Amplified outputs EI and EQ of the amplifiers 54 and 53are supplied to the balanced mixers 26 and 27.

The signal e₂ supplied to the 90 degrees splitter 25 is divided into twosignals e₂₁ and e₂₂. Signal e₂₁ is in phase with signal e₂, while signale₂₂ is displaced 90 degrees with respect to signals e₂. Signals e₂₁ ande₂₂ are supplied to the balanced mixers 26 and 27, respectively.

In the mixers 26 and 27, the signal EI is mixed with E21 and signal EQis mixed with e₂₂. The outputs eI, eQ of mixers 26 and 27 are combinedby an in-phase combiner 28 so that an output signal e_(o) is generatedat output terminal 8.

Now, if the first and second signals e₁ and e₂ are defined by:

    e.sub.1 =cos wt; and e.sub.2 =cos(wt+θ),

then the output EI of the mixer 41 is described by the followingequation: ##EQU1## Hence, if the output voltage EI is passed through thelow-pass filter 51, then the output voltage EI is obtained in thefollowing equation:

    EI=1/2 cos θ

The output EI of the inverse amplifier 54 connected with the outputterminal of the low-pass filter 51 is obtained in the following equationif its amplification is -2:

    EI=-cos θ

On the other hand, the output voltage EQ generated by the mixer 42 isdefined by the following equation: ##EQU2## Hence, if this voltage EQ isapplied to the low-pass fi1ter 52, the output voltage EQ is obtained inaccordance with the following equation: ##EQU3## Applying this output ofthe low-pass filter 52 to the in-phase amplifier 53, the output EQ ofthe amplifier 53 is obtained in the following equation if itsamplification is 2:

    EQ=sin θ

Since the mixer 26 mixes the output EI with signal e₂₁, its output eI isexpressed in the following equation:

    eI=-cos θ. cos (wt+θ)

On the other hand, since the mixer 27 mixes the output EQ with signale₂₂, its output eQ is expressed in the following form: ##EQU4##

After these outputs are combined by the combiner 28, the output e_(o) isexpressed in the following equation: ##EQU5## As a result, the outputsignal e_(o) is controlled to have its phase inverted from that of thefirst signal e₁.

In this case gain of amplifier 54 may be made positive whereupon thesignal e₂₁ should be supplied to the mixer 26 after its polarity hasbeen reversed.

As has been described hereinbefore, according to the present invention,one of the two signals having a phase difference is shifted to have theopposite polarity in regardless with the phase of one signal.

It will be apparent to those skilled in the art that variousmodifications and variations could be made to the embodiment of theinvention as hereinabove described without departing from the spirit andscope of the invention.

What is claimed is:
 1. A phase shifter comprising:first and secondterminals for receiving first and second signals having a phasedifference from each other; first mixing means for mixing said firstsignal with said second signal; means for displacing the phase of saidfirst signal by 90 degrees to produce a first phase-displaced signal;second mixing means for mixing said first phase-displaced signal withsaid second signal; third mixing means for mixing said second signalwith an output signal provided from said first mixing means; means fordisplacing the phase of said second signal by 90 degrees to produce asecond phase-displaced signal; fourth mixing means for mixing saidsecond phase-displaced signal with an output signal provided from saidsecond mixing means; and combining means for combining an output signalof said third mixing means with an output signal provided from saidfourth mixing means to generate a signal which has a phase opposite tothat of said first signal.
 2. The phase shifter as defined in claim 1wherein first and second low-pass filters and amplifiers inserial-relation to each other are inserted between said first mixermeans and said third mixer means and between said second mixer means andsaid fourth mixer means, respectively.
 3. The phase shifter as definedin claim 2 wherein said first and second amplifiers have inversepolarity gains with respect to each other.